AD7873 Input Touch Screen Digitizer Linux Driver

Supported Devices

Description

The AD7843/AD7873 is a 12-bit successive-approximation ADC with a synchronous serial interface and low on resistance switches for driving touch screens. The parts operates from a single 2.2 V to 5.25 V power supply and features throughput rates greater than 125 kSPS.
The external reference applied to the AD7843 can be varied from 1 V to +VCC, while the analog input range is from 0 V to VREF. The device includes a shutdown mode that reduces the current consumption to less than 1 µA.

The AD7873 is similar to the AD7843 but has added functionality such as an on-chip temperature sensor (-40°C to + 85°C), on-chip 2.5 V reference and direct battery and touch-pressure measurement.

Configuration

Software configurable features

Source Code

Status

Files

Example platform device initialization

For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.

For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.

Declaring SPI slave devices

Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.

This method is appropriate when the SPI bus is a system bus, as in many embedded systems, wherein each SPI bus has a number which is known in advance. It is thus possible to pre-declare the SPI devices that inhabit this bus. This is done with an array of struct spi_board_info, which is registered by calling spi_register_board_info().

Page Tools

ADI enables our customers to interpret the world around us by intelligently bridging the physical and digital with unmatched technologies that sense, measure and connect. We collaborate with our customers to accelerate the pace of innovation and create breakthrough solutions that are ahead of what’s possible.

Interested in the latest news and articles about ADI products, design tools, training and events? Choose from one of our 12 newsletters that match your product area of interest, delivered monthly or quarterly to your inbox.